This invention concerns a III(A)-V(A) type semiconductor luminescent diode, possessing a highly doped p+ region, i.e., having an impurity concentration greater than about 4.times.10.sup.19 atoms/cc, a highly doped n+ region, i.e., having an impurity concentration greater than about 10.sup.18 atoms/cc, and an intermediate p radiative recombination region, in which the radiation light is emitted in the plane of the PN-junction. The radiative layer of such diodes is narrow seen from the side, the width being about 20 microns; said layer possesses a high luminous density.
The current injected into such a diode is modulated for information transmission, in which -- and in many other applications -- the recombination delay time between discrete points has to be constant.
III(A)-V(A) type semiconductor electroluminescent diodes are generally known. The luminescence in such diodes originates in the vicinity of a PN-junction, due to recombination of electrons with defect electrons, which occurs under light emission. Numerous investigations have already been carried out concerning an increase of the light emitting efficiency. The following results have been obtained.
In order to decrease the absorption by free charge carriers due to the high carrier injection, the compensation within the radiative layer has to be comparatively high (N.sub.A .apprxeq.N.sub.D).
The presence of nearly the same number of both donors and acceptors within the radiative layer results in "shallow" acceptor dopant gradients.
The recombination layer of high compensation degree inserted between the p and N layers, has to be chosen at least as large as the distance of diffusion (L.sub.n) of the injected carriers.
Under the condition of equal interior quantum efficiencies, the luminescence intensity of the radiation from the active layer is -- due to absorption and leakage -- higher when laterally emitting compared to a PN-layer-traversing radiation.
The light modulation by means of the injection current permits the application of such diodes in a simple transmission system.
Measurements have been carried out on conventional luminescent diodes with respect to the delay times between excitation and light emission.
The differences in the results of the measurements of the light emitted parallel to the PN-junction differed from those perpendicular to the junction reaches up to about 10.sup. -8 seconds. Diodes suffering from such magnitudes of local differences in delay time cannot find application in precision distance measuring devices, operating on the radar principle.
Large local differences in the delay time result in severe deteriorations of the exactness of the measuring results. If one considers such local deviations in respect to the delay time, coupled emitter circuits, which, for example, are employed in logic optimum operations, or optical signal storing, or emitted-radiation-into-intensity-oscillation conversion, are only applicable for frequencies below 10.sup.8 Hz.
Owing to this fact, the advantage inherent in luminescent diodes, namely to modulate up to very high frequencies, cannot be exploited. Differences in injection and absorption within the active layer affect the magnitude of the local differences in delay time, which in turn cause the aforementioned disadvantages. Said disadvantages are not restricted to laterally emitting electroluminescent diodes but also occur with those having PN-layer-traversing radiation.